The present invention relates to an ultrasonic assisted process for bringing about in situ chemical interaction between at least a small portion of the individual polymer components within a blend of at least two polymers. More particularly, the present invention relates to a process creating chemical interactions between at least two polymers by ultrasonic treatment of a mixture of such polymers during or after mixing using continuous or batch mixers. In the process of the present invention, an unexpected chemical phenomenon occurs that enhances or improves the mechanical properties of these polymer blends when compared with identical polymer blends not subjected to the ultrasonic treatment.
Blending polymers is a useful approach for the preparation of new materials with specially tailored or improved properties that are often absent in the single component polymers. Enhanced properties of polymeric materials are achieved by developing multi-component systems in the form of polymer blends composed of two or more homopolymers. However, many polymer pairs are incompatible or immiscible with each other and exhibit either very low or no interfacial adhesion and phase separate on blending. The mechanical properties of polymer blends are strongly influenced by the strength of the interfaces between the different phases, as well as the dispersion and interaction between them.
In most cases, mixing of two dissimilar polymers results in blends that are weak and brittle. It is commonly known that, in order to achieve compatibilization, a third component, typically a block copolymer, may be added to the system. The addition of a pre-made block copolymer to an otherwise immiscible or incompatible polymer blend can lead to a reduction of interfacial tension. Such block copolymers are selected to contain blocks chemically identical to the components within the polymer blend, thereby assuring miscibility between the copolymer segments and the corresponding blend components at the interface.
Alternatively, forming blends of two or more dissimilar polymers may be achieved through an in situ chemical reaction using specifically selected or specifically tailored chemicals. This is generally known as reactive blending. Reactive blending typically relies on either the in situ formation of copolymers or the surface interaction of polymers using specifically selected or specifically tailored chemicals. The blend components themselves are chosen or modified so that reaction occurs during melt blending. Also, existing technologies for making plastic/rubber blends involve compounding components with the aid of chemicals (compatibilizers or coupling agents) or dynamic vulcanization of rubber phase components with the aid of curatives. These generally known processes, briefly introduced above, lead to modification of the polymer interfaces in multi-phase blends, and thereby to tailoring of the phase structure, and hence properties. However, these methods are restrictive in that different, specifically tailored chemicals or copolymers are required for different polymer mixtures.
Notably, economic factors play an important part in deciding how to prepare polymer blends. Those of ordinary skill in the art appreciate that existing technologies, employing specifically tailored or specially selected block copolymers and/or compatibilizers, coupling agents, or curatives, are neither optimally time effective nor cost effective.
Thus, the ability to make virtually any two or more polymers compatible with each other to produce polymer blends and copolymers exhibiting desirable mechanical properties is the focus of the present invention. The ultimate goal of polymer blending according to the present invention is a practical one of achieving commercially viable products exhibiting desirable properties at low cost. Additionally, through practice of the present invention, the recycling of various polymers and/or polymer products may also be greatly enhanced in that used polymers can be combined to achieve desirable chemical and physical properties.
In general, the present invention provides an efficient process for the production of novel polymer blends and copolymers. The process includes feeding at least two polymers to a pressurized treatment zone and treating the at least two polymers with ultrasonic waves in the pressurized treatment zone. The at least two polymers are selected from the group consisting of thermoplastics, thermosets, rubbers, and liquid crystalline polymers (LCP""s).
Advantageously, the present invention overcomes the problems associated with the prior art of chemical compatibilization of polymer blends by treating blends of polymers, with ultrasound either during or after mixing using continuous-type or batch-type mixers. It is known that the mechanical properties of such blends depend upon the adhesion between components as well as the dispersion and interaction between them. After the ultrasonic treatment of such blends during extrusion, an unexpected phenomenon is found, namely, significant enhancement of mechanical properties, such as tensile strength, modulus, elongation at break and toughness, in comparison with blends not subjected to ultrasound.
Experimental data supports a conclusion that new copolymers or graft polymers are created from the blended polymers at the interface and at the vicinity of the interface between the polymers after only a very short time (in the order of a few seconds) of ultrasonic treatment under high pressures and temperatures above the melting point or glass transition temperature of the polymers, because the enhancement of mechanical properties realized for such blends after ultrasonic treatment thereof indicates that more than a simple mix of polymers is being produced. Surprisingly, these copolymers are obtained for pairs of polymers that otherwise cannot be polymerized into copolymers since they are incompatible or immiscible with each other. Thus, it is believed that this invention makes it possible to create new copolymers or graft polymers from practically any pairs of existing polymers, and such copolymers or graft polymers may be created with desirable resultant physical properties.
In the present invention, novel polymer blends are prepared through an in situ chemical interaction resulting from ultrasonic treatment. By xe2x80x9cin situ chemical interactionxe2x80x9d it is meant any chemical (i.e. non-physical or mechanical) interaction wherein at least a portion of the polymers blended are chemically linked via a chemical reaction. In particular, experimental evidence supports the conclusion that this in situ chemical interaction forms copolymers or grafted polymers at least a portion of the interface between the blended polymers. Generally, only a fraction of the at least two polymers blended undergo this in situ chemical interaction.
Unexpectedly, the ultrasonic treatment of polymer blends, during or after mixing, is found to greatly improve their mechanical properties. The present invention also proposes continuous and batch processes for carrying out in situ chemical interactions without adding chemicals. It is believed that ultrasonic treatment of the blends enhances intermolecular interaction and makes chemical bonds between dissimilar polymers creating a small but effective amount of copolymer or graft copolymer without the use of any chemicals.
In general, the present invention provides a process for the in situ chemical interaction of polymer blends, including the steps of feeding to a pressurized treatment zone at least two polymers selected from the group consisting of thermoplastics, thermosets, rubbers, and liquid crystalline polymers, and ultrasonically treating the polymer mixture in the pressurized treatment zone with an ultrasonic wave.